End-to-end communication encryption is a technology for encrypting and decrypting voice/data, etc., which can implement encryption transmission of voice/data signals in air interfaces and core networks to further enhance security of communication. The end-to-end encrypted communication is usually called as scrambled session, and the non-encrypted communication is called as clear session. With the development of secure communication technology, free switch between the clear session and the scrambled session has become the requirement for users at both sides of communication. Most of currently known clear session and scrambled session switch technologies need cooperation of terminals and network devices, or control switch through end-to-end in-band signaling.
For example, Chinese patent CN200510007514 discloses a “method for realizing switch between clear session and scrambled session in end-to-end voice communication”, which is applicable to a soft switch system comprising a switch, a key distribution center, a base station controller, a public telephone switching network and an encryption gateway. When a calling party and a called party establish a call and talk normally, the method includes the following steps. After receiving a switch request, the switch determines the current talking manner, and if the current talking manner is clear session, then a switch where one party initiating the switch request is located switches the current session to scrambled session after applying a key from the key distribution center; if the current talking manner is scrambled session, then the switch where the party initiating the switch request is located sends a scrambled session closing message to a switch where another party is located and switches the current session to clear session and closes a cue tone.
Disadvantages existing in the patent is that its implementation process is relatively complex, switch between clear session and scrambled session needs cooperation of the switch, the key distribution center and the base station controller, the requirement for network devices is high, and implementation cost is high, thus real end-to-end control cannot be implemented.
As another example, Chinese patent CN200410080036 discloses “a method for realizing switch from clear session to scrambled session”, which comprises the following steps. A first terminal sends a scrambled session service transferring request to a second terminal, and notifies the second terminal to start scrambled session service negotiation with the network side, while the first terminal starts scrambled session service negotiation with the network side; after a scrambled session transmission channel is established, a scrambled session talking process is performed between the first terminal and second terminal. According to this method, first the scrambled session service negotiation between the terminals is transferred, and then a scrambled session transparent transmission channel is established to guarantee smooth implementation of switch from clear session to scrambled session. In addition, the patent further proposes process control which can implement switch from clear session to scrambled session through in-band signaling. Thus, any influence on existing networks will not be caused, and cooperation of the existing networks is not required. If there are private networks superposing on universal networks, then each private network can define a signaling structure by itself, and can expand signaling content arbitrarily to provide great convenience for the private networks and the universal networks.
However, the above-mentioned patents have some disadvantages: 1) the switch process still needs cooperation of the networks, terminals at both sides of the communication are required to complete scrambled session negotiation with the network side respectively, thus end-to-end control cannot be implemented really; 2) the switch control process uses in-band signaling, such as dual tone multi frequency (DTMF), and information carried in the voice in-band signaling is limited (for example, only one bit data can be sent every time), and the transmission efficiency is low, thus resulting in a longer switch process.